1. Field of the Invention
The present invention relates to an apparatus and a method for calculating a fatigue usage factor with respect to fatigue generated in the material of a mechanical device depending upon changes of an operation environment during operation of the mechanical device, and more particularly to an apparatus and a method for calculating a fatigue usage factor at an increased accuracy by reflecting any actual changes of the operation environment into the calculation of the fatigue usage factor.
2. Description of the Related Art
In general, a mechanical device is affected by changes of operation parameters, such as temperature, pressure, flow rate or the like, in accordance with operational conditions while being operated, which may cause fatigue in the material constituting the mechanical device. Such fatigue can be numerically calculated through engineering calculations, and on the basis of that a lifespan of the mechanical device can be predicted.
However, in a method for numerically calculating fatigue generated in the mechanical device using conventional technologies, a value of fatigue has been overestimated. Therefore, it is noted that the expected lifespan of the mechanical device which is calculated on the basis of the overestimated fatigue value may be shortened.
Equation 1 refers to a formula for calculating a cumulative fatigue usage factor with respect to fatigue generated in the mechanical device. The cumulative fatigue usage factor is represented by a sum of each fatigue usage factor to be calculated for respective transient states (1, 2, . . . , n). That is,
                              ∑          1          n                ⁢                  =                                    U                              transient                ⁢                                                                  ⁢                1                                      +                          U                              transient                ⁢                                                                  ⁢                2                                      +            …            +                          U                              transient                ⁢                                                                  ⁢                n                                                                        (        1        )            
wherein “ΣUtransient n” denotes the cumulative fatigue usage factor at an arbitrary transient state n.
The term “transient” refers to a status where the operation parameters, such as temperature, pressure, flow rate or the like, are continuously varying in accordance with lapse of time due to changes of the operational condition of the mechanical device.
Equation 2 is a formula for calculating a fatigue usage factor according to the conventional calculation method. The cumulative fatigue usage factor at an arbitrary transient state n is calculated by adding a fatigue usage factor, which is calculated on the basis of a design-transient state, to a cumulative fatigue usage factor which is accumulated till the occurrence of the arbitrary transient state n. That is,ΣUtransient n=ΣU0.transient n+UDSGN.cyc.transient n  (2)
wherein “ΣUtransient n” refers to a cumulative fatigue usage factor at an arbitrary transient state n, “ΣU0.transient n” denotes a cumulative fatigue usage factor accumulated till the occurrence of the arbitrary transient state n, and “UDSGN.cyc,transient n” means a fatigue usage factor calculated on the basis of condition of a design-transient state.
The term “design-transient state” is a transient status defined at the design stage of the mechanical device, which refers to changes of the operation parameters expected to be made during the operation period.
In the conventional calculation method hereinabove, as shown in Equation 2, since the fatigue usage factor which corresponds to the design-transient state is calculated and used even if any operation-transient state occurs, the calculated value of the fatigue usage factor might be greater than that of the actual fatigue usage factor. Consequently, it has drawbacks in that the cumulative fatigue usage factor according to Equation 1 increases, and simultaneously the expected lifespan of the mechanical device is shortened.